content: /*
   * Copyright 2016-present David Karnok
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package hu.akarnokd.rxjava3.operators;
  
  import java.util.Objects;
  import java.util.concurrent.atomic.*;
  
  import io.reactivex.rxjava3.core.*;
  import io.reactivex.rxjava3.disposables.Disposable;
  import io.reactivex.rxjava3.exceptions.Exceptions;
  import io.reactivex.rxjava3.functions.Function;
  import io.reactivex.rxjava3.internal.disposables.DisposableHelper;
  import io.reactivex.rxjava3.internal.util.AtomicThrowable;
  
  /**
   * FlatMap only one {@link ObservableSource} at a time and ignore upstream values until it terminates.
   * @param <T> the upstream value type
   * @param <R> the output type
   * @since 0.19.0
   */
  final class ObservableFlatMapDrop<T, R> extends Observable<R> implements ObservableTransformer<T, R> {
  
      final Observable<T> source;
  
      final Function<? super T, ? extends ObservableSource<? extends R>> mapper;
  
      ObservableFlatMapDrop(Observable<T> source,
              Function<? super T, ? extends ObservableSource<? extends R>> mapper) {
          this.source = source;
          this.mapper = mapper;
      }
  
      @Override
      public ObservableSource<R> apply(Observable<T> upstream) {
          return new ObservableFlatMapDrop<>(upstream, mapper);
      }
  
      @Override
      protected void subscribeActual(Observer<? super R> observer) {
          source.subscribe(new FlatMapDropObserver<T, R>(observer, mapper));
  
      }
  
      static final class FlatMapDropObserver<T, R>
      implements Observer<T>, Disposable {
  
          final Observer<? super R> downstream;
  
          final Function<? super T, ? extends ObservableSource<? extends R>> mapper;
  
          final FlatMapDropInnerObserver innerObserver;
  
          final AtomicThrowable errors;
  
          final AtomicInteger done;
  
          Disposable upstream;
  
          volatile boolean active;
  
          FlatMapDropObserver(Observer<? super R> downstream,
                  Function<? super T, ? extends ObservableSource<? extends R>> mapper) {
              this.downstream = downstream;
              this.mapper = mapper;
              this.innerObserver = new FlatMapDropInnerObserver();
              this.errors = new AtomicThrowable();
              this.done = new AtomicInteger(1);
          }
  
          @Override
          public void onSubscribe(Disposable d) {
              if (DisposableHelper.validate(upstream, d)) {
                  this.upstream = d;
                  downstream.onSubscribe(this);
              }
          }
  
          @Override
          public void onNext(T t) {
              if (!active) {
                  ObservableSource<? extends R> o;
  
                  try {
                      o = Objects.requireNonNull(mapper.apply(t), "The mapper returned a null ObservableSource");
                  } catch (Throwable ex) {
                      Exceptions.throwIfFatal(ex);
                      upstream.dispose();
                      onError(ex);
                      return;
                  }
  
                  active = true;
                  done.incrementAndGet();
                  o.subscribe(innerObserver);
              }
          }
  
          @Override
          public void onError(Throwable e) {
              if (errors.tryAddThrowableOrReport(e)) {
                  onComplete();
              }
          }
  
          @Override
          public void onComplete() {
              if (done.decrementAndGet() == 0) {
                  errors.tryTerminateConsumer(downstream);
              }
          }
  
          @Override
          public void dispose() {
              upstream.dispose();
              DisposableHelper.dispose(innerObserver);
              errors.tryTerminateAndReport();
          }
  
          @Override
          public boolean isDisposed() {
              return upstream.isDisposed();
          }
  
          void innerNext(R item) {
              downstream.onNext(item);
          }
  
          void innerError(Throwable e) {
              if (errors.tryAddThrowableOrReport(e)) {
                  innerComplete();
              }
          }
  
          void innerComplete() {
              active = false;
              if (done.decrementAndGet() == 0) {
                  errors.tryTerminateConsumer(downstream);
              }
          }
  
          final class FlatMapDropInnerObserver
          extends AtomicReference<Disposable>
          implements Observer<R> {
  
              private static final long serialVersionUID = -3707363807296094399L;
  
              @Override
              public void onSubscribe(Disposable d) {
                  DisposableHelper.replace(this, d);
              }
  
              @Override
              public void onNext(R t) {
                  innerNext(t);
              }
  
              @Override
              public void onError(Throwable e) {
                  innerError(e);
              }
  
              @Override
              public void onComplete() {
                  innerComplete();
              }
          }
      }
  }
  